WO2019003242A1 - Method for texturing diamond wire cut multicrystalline silicon wafers without additives - Google Patents

Method for texturing diamond wire cut multicrystalline silicon wafers without additives Download PDF

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Publication number
WO2019003242A1
WO2019003242A1 PCT/IN2018/050348 IN2018050348W WO2019003242A1 WO 2019003242 A1 WO2019003242 A1 WO 2019003242A1 IN 2018050348 W IN2018050348 W IN 2018050348W WO 2019003242 A1 WO2019003242 A1 WO 2019003242A1
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Prior art keywords
dwc
texturing
wafer
acid
solution
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PCT/IN2018/050348
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French (fr)
Inventor
Prabir Kanti BASU
Sreejith Koorthedath PULLAIKODI
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Indian Institute Of Technology Bombay
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Publication of WO2019003242A1 publication Critical patent/WO2019003242A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0236—Special surface textures
    • H01L31/02363—Special surface textures of the semiconductor body itself, e.g. textured active layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic Table
    • H01L31/182—Special manufacturing methods for polycrystalline Si, e.g. Si ribbon, poly Si ingots, thin films of polycrystalline Si
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/546—Polycrystalline silicon PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the embodiments herein relate to texturing silicon wafers and more particularly relates to a method for texturing diamond wire cut multicrystalline silicon wafers without additives.
  • the present application is based on, and claims priority from an Indian Application Number 201721022615 filed on 28 th June, 2017 the disclosure of which is hereby incorporated by reference herein.
  • multicrystalline silicon wafers are used for fabrication of Micro-Electro-Mechanical Systems (MEMs), photovoltaic solar cells and so on.
  • MEMs Micro-Electro-Mechanical Systems
  • the wafer is used as the substrate over which other micro fabrication processes like doping or ion implantation, etching, deposition of various materials, screen printing and photolithographic patterning are conducted.
  • the silicon wafers can be slurry cut or diamond wire cut.
  • slurry cut technique chemicals are used to form slurry. Wires are passed through the slurry which is used to cut the silicon wafers. The kerf loss in case of slurry cut silicon wafers is very large.
  • the diamond wire cut silicon wafer cutting process involves cutting multicrystalline silicon ingot into wafers using wires coated with diamond particles.
  • isotropic texturing using acid solution is commonly used in the fabrication of multicrystalline silicon (multi-Si) wafers. This texturing process generates rounded structures on the wafer surface and thus improves light absorption.
  • isotropic texturing using acid solution can only texture slurry cut (SC) raw multi-Si wafers.
  • Diamond wire cut (DWC) multi-Si wafers are highly polished. Since multi-Si texturing process nucleates along the damaged Si surface as a seeding layer, the conventional isotropic texturing using acid solution cannot be used to texture the highly polished DWC multi-Si wafers.
  • the principal object of the embodiments herein is to provide a method for acid texturing diamond wire cut (DWC) multicrystalline silicon wafers without using any additional chemical as additive.
  • DWC diamond wire cut
  • Another object of the embodiments herein is to provide acid texturing of DWC multi-Si wafers without the use any additives in the acid texturing solution.
  • Another object of the embodiments herein is to provide acid texturing of DWC multi-Si wafersusing a predefined composition of HF and HN0 3 acids in the acid texturing solution.
  • Another object of the embodiments herein is to use a very dilute solution of 0.5%- 1% of the alkali for dissolving the porous- Si formed over a raw DWC multi-Si wafer.
  • Another object of the embodiments herein is to use a very dilute alkali solution with a smaller etching time which prevents anisotropic Si-etch by the alkali for the multi-Si wafers.
  • Another object of the embodiments herein is to provide a method which reduces metal contamination of the wafer surface by using a diluted alkali solution.
  • the embodiments herein provide a method for texturing diamond wire cut (DWC) multicrystalline silicon (multi-Si) wafer.
  • the method includes preparing an acid texturing solution with a specific concentration of nitric acid and hydrofluoric acid. Further, the method includes forming a porous-Si layer by treating the DWC multi-Si wafer with the acid texturing solution for a pre-determined time interval and at a predetermined temperature. The method also includes dissolving the porous-Si layer by dipping the DWC multi-Si wafer surface in an alkali solution for DWC multi-Si wafer texturing.
  • a composition of hydrofluoric acid and nitric acid in the acid texturing solution is varied in ratios between 15: 1 to 15:3 based on a volume of deionized (DI) water in the acid texturing solution.
  • DI deionized
  • the DWC multi-Si wafer is treated with the acid texturing solution for the pre-determined time interval of 2-5 minutes and at the pre-determined temperature of 10-15°C to form the porous-Si layer.
  • the pre-determined time interval of 2-5 minutes is varied based on chemical composition, solution temperature, effect of incident light and nature of chemicals.
  • the alkali solution has a concentration of 0.5%- 1% KOH, wherein the DWC multi-Si wafer surface is dipped in the alkali solution for 2-5 seconds at a room temperature of 25°C.
  • the alkali solution with a smaller etching time prevents anisotropic Si-etch by the alkali for the multi-Si wafer.
  • a volume of Si-etching is greater than 1.8 ⁇ during formation of porous-Si layer.
  • metal-ion neutralization is performed in a mixture comprising hydrochloric acid and hydrofluoric acid (HF) at a room temperature for a textured DWC multi-Si wafer.
  • the textured DWC multi-Si wafer has a less reflective texturing surface.
  • a textured DWC multi-Si wafer product can be manufactured by performing the method as described above.
  • FIG. 1 is a schematic illustrating a process flow for acidic texturing of DWC multi-Si wafers using additives in an existing mechanism, according to an embodiment as disclosed herein;
  • FIG. 2 is a schematic illustrating a process flow for acidic texturing DWC multi-Si wafers using metal assisted etching (MAE) in an existing mechanism, according to an embodiment as disclosed herein;
  • MAE metal assisted etching
  • FIG. 3 is a flow chart illustrating a method for texturing DWC multi-Si wafers, according to an embodiment as disclosed herein;
  • FIG. 4 is a schematic illustrating a process flow for texturing
  • FIG. 5A illustrates raw (as-cut) multi-Si wafers before acid texturing, according to an embodiment as disclosed herein;
  • FIG. 5B illustrates textured DWC multi-Si wafers after acid texturing, according to an embodiment as disclosed herein;
  • FIG. 6 is a graph showing variation of textured surface reflectance (%) versus wavelength (nm) with weighted average reflectance (WAR) values for as-cut DWC multi-Si wafers, standard acid-textured slurry cut multi-Si wafers and textured DWC multi-Si wafers, according to an embodiment as disclosed herein; and
  • FIGS.7A-7B illustrates scanning electron microscope (SEM) images of textured DWC multi-Si wafers, according to an embodiment as disclosed herein.
  • the embodiments herein provide a method for diamond wire cutting (DWC) multicrystalline silicon (multi-Si) wafer texturing.
  • the method includes preparing an acid texturing solution comprising of a specific concentration of nitric acid and hydrofluoric acid. Further, the method includes forming a porous-Si layer by treating the DWC multi-Si wafer with the acid texturing solution for a pre-determined time interval and at a pre-determined temperature. The method also includes dissolving the porous-Si layer by dipping the DWC multi-Si wafer surface in an alkali solution for DWC multi-Si wafer texturing.
  • a textured DWC multi-Si wafer product can be manufactured by performing the method as described above.
  • multi-Si wafer texturing nucleates along the damaged Si surface as a seeding layer which cannot efficiently texture the highly polished DWC multi-Si wafers.
  • MCT metal catalyst texturing
  • AgN03 silver nitrate
  • the proposed method does not use any additives in form of acids or solvents in the acid texturing solution.
  • the proposed method uses the acid texturing solution of HF and HN03 acids in a specific concentration for multi-Si wafer texturing.
  • the proposed method uses a very dilute alkali solution with a smaller etching time which prevents anisotropic Si-etch by the alkali for the multi-Si wafers.
  • the proposed method reduces the metal contamination of the wafer surface by using diluted alkali solution.
  • FIGS. 1 through 7 where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.
  • FIG. 1 is a schematic illustrating process flow for acidic texturing of DWC multi-Si wafers using additives in an existing mechanism, according to an embodiment as disclosed herein.
  • the raw DWC multi-Si wafer is the base material.
  • the acid texturing solution contains hydrofluoric acid (HF) - nitric acid (HN03).
  • the raw DWC multi-Si wafer is treated with the acid texturing solution which contains additives like polyvinyl alcohol, phosphoric acid and sulphuric acid leading to the formation of porous Si. Further, the porous Si is removed by dissolving it with a dilute alkali solution.
  • the wafer is then subjected to metal-ion neutralization clean using HF/HCl based process to obtain the final textured wafer.
  • FIG. 2 is a schematic illustrating process flow for acidic texturing using metal assisted etching (MAE) in an existing mechanism, according to an embodiment as disclosed herein.
  • MAE metal assisted etching
  • the raw DWC multi-Si wafer is the base material.
  • the DWC multi-Si wafer is subjected to saw-damage etching (SDE) using high concentration of alkali solution. Further, the wafer is subjected to metal assisted etching using HF/H202/AgN03 solution.
  • SDE saw-damage etching
  • metal assisted etching using HF/H202/AgN03 solution.
  • the conventional acid solution treatment of the wafer leads to the formation of porous Si. Further, the porous Si is removed by dissolving it with a dilute alkali solution.
  • the wafer is then subjected to metal-ion neutralization cleaning using HF/HC1 based process to obtain the final textured wafer.
  • FIG. 3 is a flow chart 300 illustrating a method for texturing DWC multi-Si wafers, according to an embodiment as disclosed herein.
  • the acid texturing solution comprises of a specific concentration of nitric acid and hydrofluoric acid i.e., concentration in the range 15: 1 tol5:3.
  • the DWC multi-Si wafer is treated with the acid texturing solution for a pre-determined time interval and at a pre-determined temperature to from the porous Si layer i.e., for the pre-determined time interval of 2-5 minutes and at the pre-determined temperature of 10-15°C to form the porous Si layer.
  • the porous-Si layer is dissolved by dipping the DWC multi-Si wafer surface in a dilute alkali solution of 0.5%- 1% KOH.
  • the DWC multi-Si wafer is subjected to metal-ion neutralization by treating it with HF/HC1 to obtain the final low reflective textured silicon wafer.
  • a textured DWC multi-Si wafer product can be manufactured by performing the steps S302-S308 of the flow diagram 300 as illustrated in the FIG.3.
  • FIG. 4 is a schematic illustrating process flow for texturing DWC multi-Si wafers using the specific composition of HF and HN0 3 acids, according to an embodiment as disclosed herein.
  • the raw DWC multi-Si wafer is brought in contact with acid texturing solution containing hydrofluoric acid (HF) - nitric acid (HN03) in a specific combination for a predefined time and at a predefined temperature, which leads to the formation of porous-Si.
  • HF hydrofluoric acid
  • HN03 hydrofluoric acid
  • the concentration of HF and HN03 can be in the range 15: 1 to 15:3.
  • the concentration is based on the amount of DI water in the textured solution which enables the porous-Si growth needed for the rounded textured multi-Si wafer surface.
  • the temperature range is maintained between 10-15°C.
  • the time taken for the growth of porous-Si growth can be within 2-5 min based on the chemical composition, solution temperature, effect of incident light and the nature of chemical bath.
  • the amount of Si-etching (>1.8 ⁇ from each side) during this porous- Si growth process is sufficient for the saw damage removal of the multi-Si wafers.
  • the porous Si is removed by dissolving it with a very dilute alkali solution i.e., 0.5%-l% KOH solution, at a room temperature of ⁇ 25°C by dipping it for 2-5 sec.
  • the very dilute alkali solution with a smaller etching time prevents anisotropic Si-etch by the alkali for the multi-Si wafers. Further, the dilution reduces metal contamination of the wafer surface as compared to the existing industrial process.
  • the wafer is then subjected to metal-ion neutralization clean using HF/HC1 based process to obtain the final textured wafer.
  • FIG. 5A illustrates raw (as-cut) multi-Si wafers before texturing, according to an embodiment as disclosed herein.
  • FIG. 5B illustrates textured DWC multi-Si wafers after texturing, according to an embodiment as disclosed herein.
  • FIG. 6 is a graph showing variation of reflectance (%) versus wavelength (nm) with WAR values for as-cut DWC multi-Si wafers, standard acid-textured slurry cut multi-Si wafers and textured DWC multi- Si wafers, according to an embodiment as disclosed herein.
  • the weighted average reflectance (WAR) is calculated based on AM 1.5 spectra in the 300-1000 nm wavelength range of the incident light.
  • the graph illustrates a drastic reduction of surface reflectance from the as-cut DWC wafer using additive free texturing process.
  • the additive free texturing process resulted in a lesser WAR value as compared to the conventional acid-textured SC multi-Si wafers.
  • FIGS.7A-7B illustrates scanning electron microscope (SEM) images of textured DWC multi-Si wafers, according to an embodiment as disclosed herein.
  • FIG.7A and FIG.7B the scanning electron microscope (SEM) images of the textured DWC multi-Si wafers are illustrated.
  • the rounded features of the textured DWC multi-Si wafer surface are visible in FIG.7A and FIG.7B, illustrating the axial view and angular view SEM images of the textured DWC multi-Si wafers.

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Abstract

Embodiments herein provide a method for diamond wire cutting (DWC) multicrystalline silicon (multi-Si) wafer texturing. The method includes preparing an acid texturing solution comprising of a specific concentration of nitric acid and hydrofluoric acid. Further, the method includes forming a porous-Si layer by treating the DWC multi-Si wafer with the acid texturing solution for a pre-determined time interval and at a pre-determined temperature. The method also includes dissolving the porous-Si layer by dipping the DWC multi-Si wafer surface in an alkali solution for DWC multi- Si wafer texturing.

Description

METHOD FOR TEXTURING DIAMOND WIRE CUT
MULTICRYSTALLINE SILICON WAFERS WITHOUT ADDITIVES
FIELD OF INVENTION
[0001] The embodiments herein relate to texturing silicon wafers and more particularly relates to a method for texturing diamond wire cut multicrystalline silicon wafers without additives. The present application is based on, and claims priority from an Indian Application Number 201721022615 filed on 28th June, 2017 the disclosure of which is hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] In general, multicrystalline silicon wafers are used for fabrication of Micro-Electro-Mechanical Systems (MEMs), photovoltaic solar cells and so on. The wafer is used as the substrate over which other micro fabrication processes like doping or ion implantation, etching, deposition of various materials, screen printing and photolithographic patterning are conducted.
[0003] The silicon wafers can be slurry cut or diamond wire cut. In slurry cut technique, chemicals are used to form slurry. Wires are passed through the slurry which is used to cut the silicon wafers. The kerf loss in case of slurry cut silicon wafers is very large. The diamond wire cut silicon wafer cutting process involves cutting multicrystalline silicon ingot into wafers using wires coated with diamond particles.
[0004] The isotropic texturing using acid solution is commonly used in the fabrication of multicrystalline silicon (multi-Si) wafers. This texturing process generates rounded structures on the wafer surface and thus improves light absorption. However, isotropic texturing using acid solution can only texture slurry cut (SC) raw multi-Si wafers.
[0005] Diamond wire cut (DWC) multi-Si wafers are highly polished. Since multi-Si texturing process nucleates along the damaged Si surface as a seeding layer, the conventional isotropic texturing using acid solution cannot be used to texture the highly polished DWC multi-Si wafers.
[0006] The above information is presented as background information only to help the reader to understand the present invention. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as prior art with regard to the present application.
OBJECT OF INVENTION
[0007] The principal object of the embodiments herein is to provide a method for acid texturing diamond wire cut (DWC) multicrystalline silicon wafers without using any additional chemical as additive.
[0008] Another object of the embodiments herein is to provide acid texturing of DWC multi-Si wafers without the use any additives in the acid texturing solution.
[0009] Another object of the embodiments herein is to provide acid texturing of DWC multi-Si wafersusing a predefined composition of HF and HN03acids in the acid texturing solution.
[0010] Another object of the embodiments herein is to use a very dilute solution of 0.5%- 1% of the alkali for dissolving the porous- Si formed over a raw DWC multi-Si wafer.
[0011] Another object of the embodiments herein is to use a very dilute alkali solution with a smaller etching time which prevents anisotropic Si-etch by the alkali for the multi-Si wafers.
[0012] Another object of the embodiments herein is to provide a method which reduces metal contamination of the wafer surface by using a diluted alkali solution.
SUMMARY
[0013] Accordingly the embodiments herein provide a method for texturing diamond wire cut (DWC) multicrystalline silicon (multi-Si) wafer. The method includes preparing an acid texturing solution with a specific concentration of nitric acid and hydrofluoric acid. Further, the method includes forming a porous-Si layer by treating the DWC multi-Si wafer with the acid texturing solution for a pre-determined time interval and at a predetermined temperature. The method also includes dissolving the porous-Si layer by dipping the DWC multi-Si wafer surface in an alkali solution for DWC multi-Si wafer texturing.
[0014] In an embodiment, a composition of hydrofluoric acid and nitric acid in the acid texturing solution is varied in ratios between 15: 1 to 15:3 based on a volume of deionized (DI) water in the acid texturing solution.
[0015] In an embodiment, the DWC multi-Si wafer is treated with the acid texturing solution for the pre-determined time interval of 2-5 minutes and at the pre-determined temperature of 10-15°C to form the porous-Si layer.
[0016] In an embodiment, the pre-determined time interval of 2-5 minutes is varied based on chemical composition, solution temperature, effect of incident light and nature of chemicals.
[0017] In an embodiment, the alkali solution has a concentration of 0.5%- 1% KOH, wherein the DWC multi-Si wafer surface is dipped in the alkali solution for 2-5 seconds at a room temperature of 25°C.
[0018] In an embodiment, the alkali solution with a smaller etching time prevents anisotropic Si-etch by the alkali for the multi-Si wafer.
[0019] In an embodiment, a volume of Si-etching is greater than 1.8 μηι during formation of porous-Si layer.
[0020] In an embodiment, metal-ion neutralization is performed in a mixture comprising hydrochloric acid and hydrofluoric acid (HF) at a room temperature for a textured DWC multi-Si wafer.
[0021] In an embodiment, the textured DWC multi-Si wafer has a less reflective texturing surface. [0022] A textured DWC multi-Si wafer product can be manufactured by performing the method as described above.
[0023] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF FIGURES
[0024] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0025] FIG. 1 is a schematic illustrating a process flow for acidic texturing of DWC multi-Si wafers using additives in an existing mechanism, according to an embodiment as disclosed herein;
[0026] FIG. 2 is a schematic illustrating a process flow for acidic texturing DWC multi-Si wafers using metal assisted etching (MAE) in an existing mechanism, according to an embodiment as disclosed herein;
[0027] FIG. 3 is a flow chart illustrating a method for texturing DWC multi-Si wafers, according to an embodiment as disclosed herein;
[0028] FIG. 4 is a schematic illustrating a process flow for texturing
DWC multi-Si wafers using a specific composition of HF and HN03 acids, according to an embodiment as disclosed herein;
[0029] FIG. 5Aillustrates raw (as-cut) multi-Si wafers before acid texturing, according to an embodiment as disclosed herein; [0030] FIG. 5B illustrates textured DWC multi-Si wafers after acid texturing, according to an embodiment as disclosed herein;
[0031] FIG. 6 is a graph showing variation of textured surface reflectance (%) versus wavelength (nm) with weighted average reflectance (WAR) values for as-cut DWC multi-Si wafers, standard acid-textured slurry cut multi-Si wafers and textured DWC multi-Si wafers, according to an embodiment as disclosed herein; and
[0032] FIGS.7A-7Billustrates scanning electron microscope (SEM) images of textured DWC multi-Si wafers, according to an embodiment as disclosed herein.
DETAILED DESCRIPTION OF INVENTION
[0033] Various embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. In the following description, specific details such as detailed configuration and components are merely provided to assist the overall understanding of these embodiments of the present disclosure. Therefore, it should be apparent to those skilled in the art that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well- known functions and constructions are omitted for clarity and conciseness.
[0034] Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.
[0035] Herein, the term "or" as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0036] Accordingly the embodiments herein provide a method for diamond wire cutting (DWC) multicrystalline silicon (multi-Si) wafer texturing. The method includes preparing an acid texturing solution comprising of a specific concentration of nitric acid and hydrofluoric acid. Further, the method includes forming a porous-Si layer by treating the DWC multi-Si wafer with the acid texturing solution for a pre-determined time interval and at a pre-determined temperature. The method also includes dissolving the porous-Si layer by dipping the DWC multi-Si wafer surface in an alkali solution for DWC multi-Si wafer texturing. [0037] In an embodiment, a textured DWC multi-Si wafer product can be manufactured by performing the method as described above.
[0038] In conventional methods, multi-Si wafer texturing nucleates along the damaged Si surface as a seeding layer which cannot efficiently texture the highly polished DWC multi-Si wafers.
[0039] In conventional methods, multi-Si wafer texturing has been done using additives like a solution of polyvinyl alcohol and polyethylene glycol, sulphuric or phosphoric acid etc in the hydrofluoric acid (HF) - nitric acid (HN03) texturing solution.
[0040] Conventional methods use metal catalyst texturing (MCT) using silver nitrate (AgN03) for multi-Si wafer texturing.
[0041] Conventional methods use vapor etching of Si wafers using HF/HN03 solution at 90°C for texturing.
[0042] Conventional methods also use mechanical methods with sandblasting to create surface roughness on the DWC Si wafers for texturing.
[0043] Conventional methods also use tungsten carbide tip writer to make 5-50 μιη grooves mechanically on the Si wafer surface to create texture on the DWC multi-Si wafers.
[0044] Unlike conventional methods, the proposed method does not use any additives in form of acids or solvents in the acid texturing solution.
The proposed method uses the acid texturing solution of HF and HN03 acids in a specific concentration for multi-Si wafer texturing.
[0045] Conventional methods use a 2-5% of alkali solution to dissolve the porous-Si formed according to industry standards. Unlike conventional methods, the proposed method uses a very dilute alkali solution of 0.5%- 1%
KOH to dissolve the porous-Si formed. [0046] Unlike conventional methods, the proposed method uses a very dilute alkali solution with a smaller etching time which prevents anisotropic Si-etch by the alkali for the multi-Si wafers.
[0047] Unlike conventional methods, the proposed method reduces the metal contamination of the wafer surface by using diluted alkali solution.
[0048] Referring now to the drawings, and more particularly to FIGS. 1 through 7, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.
[0049] FIG. 1 is a schematic illustrating process flow for acidic texturing of DWC multi-Si wafers using additives in an existing mechanism, according to an embodiment as disclosed herein.
[0050] Referring to FIG. 1, the process flow for acidic texturing using texturing additives in existing mechanism is illustrated. The raw DWC multi-Si wafer is the base material. The acid texturing solution contains hydrofluoric acid (HF) - nitric acid (HN03). The raw DWC multi-Si wafer is treated with the acid texturing solution which contains additives like polyvinyl alcohol, phosphoric acid and sulphuric acid leading to the formation of porous Si. Further, the porous Si is removed by dissolving it with a dilute alkali solution. The wafer is then subjected to metal-ion neutralization clean using HF/HCl based process to obtain the final textured wafer.
[0051] FIG. 2 is a schematic illustrating process flow for acidic texturing using metal assisted etching (MAE) in an existing mechanism, according to an embodiment as disclosed herein.
[0052] Referring to FIG. 2, the process flow for acidic texturing using metal assisted etching (MAE) in existing mechanism is illustrated. The raw DWC multi-Si wafer is the base material. The DWC multi-Si wafer is subjected to saw-damage etching (SDE) using high concentration of alkali solution. Further, the wafer is subjected to metal assisted etching using HF/H202/AgN03 solution. The conventional acid solution treatment of the wafer leads to the formation of porous Si. Further, the porous Si is removed by dissolving it with a dilute alkali solution. The wafer is then subjected to metal-ion neutralization cleaning using HF/HC1 based process to obtain the final textured wafer.
[0053] FIG. 3 is a flow chart 300 illustrating a method for texturing DWC multi-Si wafers, according to an embodiment as disclosed herein.
[0054] Referring to FIG. 3, at S302, the acid texturing solution is prepared. The acid texturing solution comprises of a specific concentration of nitric acid and hydrofluoric acid i.e., concentration in the range 15: 1 tol5:3.
[0055] At S304, the DWC multi-Si wafer is treated with the acid texturing solution for a pre-determined time interval and at a pre-determined temperature to from the porous Si layer i.e., for the pre-determined time interval of 2-5 minutes and at the pre-determined temperature of 10-15°C to form the porous Si layer.
[0056] At S306, the porous-Si layer is dissolved by dipping the DWC multi-Si wafer surface in a dilute alkali solution of 0.5%- 1% KOH.
[0057] At S308, the DWC multi-Si wafer is subjected to metal-ion neutralization by treating it with HF/HC1 to obtain the final low reflective textured silicon wafer.
[0058] In an embodiment, a textured DWC multi-Si wafer product can be manufactured by performing the steps S302-S308 of the flow diagram 300 as illustrated in the FIG.3.
[0059] FIG. 4 is a schematic illustrating process flow for texturing DWC multi-Si wafers using the specific composition of HF and HN03 acids, according to an embodiment as disclosed herein. [0060] Referring to FIG. 4, in an embodiment, the raw DWC multi-Si wafer is brought in contact with acid texturing solution containing hydrofluoric acid (HF) - nitric acid (HN03) in a specific combination for a predefined time and at a predefined temperature, which leads to the formation of porous-Si. In an example, the concentration of HF and HN03 can be in the range 15: 1 to 15:3. The concentration is based on the amount of DI water in the textured solution which enables the porous-Si growth needed for the rounded textured multi-Si wafer surface. The temperature range is maintained between 10-15°C. The time taken for the growth of porous-Si growth can be within 2-5 min based on the chemical composition, solution temperature, effect of incident light and the nature of chemical bath. The amount of Si-etching (>1.8μιη from each side) during this porous- Si growth process is sufficient for the saw damage removal of the multi-Si wafers. Further, the porous Si is removed by dissolving it with a very dilute alkali solution i.e., 0.5%-l% KOH solution, at a room temperature of ~25°C by dipping it for 2-5 sec. The very dilute alkali solution with a smaller etching time prevents anisotropic Si-etch by the alkali for the multi-Si wafers. Further, the dilution reduces metal contamination of the wafer surface as compared to the existing industrial process. The wafer is then subjected to metal-ion neutralization clean using HF/HC1 based process to obtain the final textured wafer.
[0061] FIG. 5A illustrates raw (as-cut) multi-Si wafers before texturing, according to an embodiment as disclosed herein.
[0062] FIG. 5B illustrates textured DWC multi-Si wafers after texturing, according to an embodiment as disclosed herein.
[0063] Referring to FIG. 5A and FIG. 5B, the raw (as-cut) and textured DWC multi-Si wafers visibly show a less reflective texturing surface after undergoing the additive free texturing process. [0064] FIG. 6 is a graph showing variation of reflectance (%) versus wavelength (nm) with WAR values for as-cut DWC multi-Si wafers, standard acid-textured slurry cut multi-Si wafers and textured DWC multi- Si wafers, according to an embodiment as disclosed herein.
[0065] Referring to FIG. 6, the surface reflectance study of the as-cut
(raw DWC), SC wafer after standard acid-texturing and the textured (DWC) multi-Si wafer surfaces is conducted using Spectrophotometer. The results are illustrated in the graph. The weighted average reflectance (WAR) is calculated based on AM 1.5 spectra in the 300-1000 nm wavelength range of the incident light.
[0066] The graph illustrates a drastic reduction of surface reflectance from the as-cut DWC wafer using additive free texturing process. The additive free texturing process resulted in a lesser WAR value as compared to the conventional acid-textured SC multi-Si wafers.
[0067] FIGS.7A-7B illustrates scanning electron microscope (SEM) images of textured DWC multi-Si wafers, according to an embodiment as disclosed herein.
[0068] Referring to FIG.7A and FIG.7B, the scanning electron microscope (SEM) images of the textured DWC multi-Si wafers are illustrated. The rounded features of the textured DWC multi-Si wafer surface are visible in FIG.7A and FIG.7B, illustrating the axial view and angular view SEM images of the textured DWC multi-Si wafers.
[0069] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

STATEMENT OF CLAIMS We claim:
1. A method for texturing diamond wire cut (DWC) multicrystalline silicon(multi-Si) wafers, the method comprising:
preparing an acid texturing solution, wherein the acid texturing solution is a mixed solution of nitric acid and hydrofluoric acid; forming a porous-Si layer by treating the DWC multi-Si wafer with the acid texturing solution for a pre-determined time interval and at a pre-determined temperature; and dissolving the porous-Si layer by dipping the DWC multi-Si wafer surface in an alkali solution for DWC multi-Si wafer texturing.
2. The method of claim 1, wherein a composition of hydrofluoric acid and nitric acid in the acid texturing solution is varied in ratios between 15:1 to 15:3 based on volume of deionized (DI) water in the acid texturing solution.
3. The method of claim 1, wherein the DWC multi-Si wafer is treated with the acid texturing solution for the pre-determined time interval of 2-5 minutes and at the pre-determined temperature of 10-15°C to form the porous-Si layer.
4. The method of claim 3, wherein the pre-determined time interval of 2- 5 minutes is varied based on chemical composition, solution temperature, effect of incident light and nature of chemicals.
5. The method of claim 1, wherein the alkali solution has a concentration of 0.5%- 1% KOH, wherein the DWC multi-Si wafer surface is dipped in the alkali solution for 2-5 seconds at a room temperature of 25°C.
6. The method of claim 5, wherein the alkali solution with a smaller etching time prevents anisotropic Si-etch by the alkali for the multi-Si wafer.
7. The method of claim 1, wherein a volume of Si-etching is greater than 1.8μιη during formation of porous-Si layer.
8. The method of claim 1, wherein metal-ion neutralization is performed in a mixture comprising hydrochloric acid and hydrofluoric acid (HF) at a room temperature for a textured DWC multi-Si wafer.
9. The method of claim 1, wherein the textured DWC multi-Si wafers has a less reflective texturing surface.
10. A diamond wire cut (DWC) multicrystalline silicon (multi-Si) wafer textured product, wherein the DWC multi-Si wafer textured product is manufactured according to claim 1.
PCT/IN2018/050348 2017-06-28 2018-05-31 Method for texturing diamond wire cut multicrystalline silicon wafers without additives WO2019003242A1 (en)

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Citations (4)

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Publication number Priority date Publication date Assignee Title
CN104328503A (en) * 2014-08-28 2015-02-04 奥特斯维能源（太仓）有限公司 Polycrystalline silicon roughening method through diamond wire cutting
US20150040983A1 (en) * 2013-08-07 2015-02-12 Solarworld Industries America, Inc. Acidic etching process for si wafers
DE102014013591A1 (en) * 2014-09-13 2016-03-17 Jörg Acker Process for the preparation of silicon surfaces with low reflectivity
CN105932078A (en) * 2016-01-15 2016-09-07 北京创世捷能机器人有限公司 Texturing method of polycrystalline silicon wafer cut by diamond wire

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20150040983A1 (en) * 2013-08-07 2015-02-12 Solarworld Industries America, Inc. Acidic etching process for si wafers
CN104328503A (en) * 2014-08-28 2015-02-04 奥特斯维能源（太仓）有限公司 Polycrystalline silicon roughening method through diamond wire cutting
DE102014013591A1 (en) * 2014-09-13 2016-03-17 Jörg Acker Process for the preparation of silicon surfaces with low reflectivity
CN105932078A (en) * 2016-01-15 2016-09-07 北京创世捷能机器人有限公司 Texturing method of polycrystalline silicon wafer cut by diamond wire

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